1. Field of the Invention
The present invention relates to technologies for detecting changes in image data generated by imaging apparatuses, such as digital cameras.
2. Description of the Related Art
In recent years, digital cameras that digitize optical images of objects and store the digitized optical images have become commercially practical. Image data photographed using such digital cameras can be easily captured in personal computers. On the other hand, such image data can be easily changed on personal computers.
Thus, image data photographed using digital cameras has a reliability lower than silver-salt photographs and has low trustworthiness. In recent years, various digital camera systems having a function to add digital signatures to image data photographed using digital cameras have been suggested.
Normally, digital signatures are generated using a public key cryptosystem, such as a Rivest Shamir Adleman (RSA) encryption. Since the public key cryptosystem, such as the RSA encryption, needs exponentiation and remainder operations, it is difficult to perform processing at a high speed, and a processing time hundreds to thousands of times that required for a common key cryptosystem, such as data encryption standard (DES), is required. Thus, it is very difficult for the limited operation resources of known digital cameras to generate digital signatures.
A method for significantly increasing the performance of operation resources of digital cameras so that digital signatures can be easily generated is available. In this method, however, the cost required for digital cameras themselves is significantly increased.
In order to solve the above problems, an image verification system capable of preventing an increase in the cost required for an imaging apparatus, such as a digital camera, and accurately detecting whether or not image data photographed using the imaging apparatus is changed is suggested in Japanese Patent Laid-Open No. 2002-244924 (U.S. publication number 2002/0060736 A1).
In the image verification system suggested in Japanese Patent Laid-Open No. 2002-244924, an image verification apparatus is separated from an imaging apparatus. The image verification apparatus accurately detects whether or not image data generated by the imaging apparatus is changed, and accurately determines whether or not image data in an image file including primary verification data is generated by the imaging apparatus. Also, if the integrity of the image file including the primary verification data is confirmed, the image verification apparatus converts the image file into an image file including secondary verification data (a digital signature).
This image verification system, however, requires the use of an apparatus, such as a personal computer, which is other than the imaging apparatus, as an image verification apparatus. Thus, a large-scale system must be used.